This invention relates to a turbomachine such as a turbine or compressor and finds use in raising the efficiency of such a turbmachine by minimizing a leakage flow from a clearance between the rotor blades and casing of the machine.
FIG. 1 is a sectional view of a gas turbine representing an example of the prior art, which is also set forth in the specification of Japanese Patent Application Laid-Open (KOKAI) No. 57-124005. The turbine, indicated by numeral 1, includes an outer casing 2, an inner casing 3, stator blades 5 and rotor blades 6 arranged in an annular flow passage 4 formed between the inner and output casings, and a casing 8 arranged at the end portion of the rotor blade 6 so as to form a clearance 7 at the end portion of the rotor blade in the radial direction.
Since the turbine inlet temperature is raised in order to improve thermal efficiency and obtain a higher specific output, it is essential that the rotor blades 6 and housing 8 be cooled. To cool the casing 8, a secondary fluid chamber 9 for a cooling fluid is formed radially outwardly of the casing 8. Such cooling enables the clearance 7 between the casing 8 and end portion of the rotor blades 6 to be held constant by suppressing the thermal expansion of these members. To further enhance the cooling effect, the aforementioned Japanese Patent Application Laid-Open No. 57-124005 discloses means for allowing the cooling fluid to flow into the clearance 7 from the secondary fluid chamber 9 through the casing 8. To achieve this, the casing 8 is provided with blow holes for discharging a secondary fluid having a component in the direction of the primary fluid flow, which is that traveling through the annular flow passage 4.
A problem encountered in the conventional arrangement is that the clearance 7 between the rotor blade 6 and casing 8 cannot be reduced to zero even if the cooling of these members is performed effectively, and there will always be a small gap in the form of the clearance 7 as long as the rotor blade 6 does not contact the casing 8. This means that some of the primary or main fluid which has entered the annular flow passage 4 flows from the clearance 7 directly to the downstream side and is not converted into rotational energy. The result is a decline in efficiency. In other words, the efficiency of a turbomachine such as the above-described turbine can be raised by sufficiently cooling the rotor blade-end casing 8 and the rotor blades 6, and by minimizing the leakage of the primary or main fluid from the clearance 7.